Figures 15-15 through 15-19 show a CBR compaction mold, fitted with a sampling collar (or cutter), and how to obtain a cylinder sample by using the CBR mold. This method may be used in taking an undisturbed sample from soft, fine-grained soils for undisturbed CBR or density tests.

When using this method, first smooth the ground surface and then press the sampling collar and mold into the soil with moderate

pressure. Then excavate a trench around the cylinder and again press the mold down over the soil, using the hand driver or loading bar if necessary. You can improvise a loading bar from any suitably sized piece of timber. Trim the soil away from the sampling collar carefully with a knife, cutting down-ward and outward to avoid cutting into the

sample. You actually do the cutting to size with the sampling collar. You can force the sampler down with the field CBR jack; however, since this jack has only about 2 in. of travel, you would do better to use a truck jack, if available. In either case, you should not force the sampler down ahead of the trimming on the outside of the cylinder. Then excavate the trench deeper and repeat the process until the soil penetrates well into the extension collar. Finally, as shown in figure 15-19, cut off the sample at the bottom of the mold with a shovel, knife, or wire, and remove the mold and sample from the hole.